Conventionally, in pursuing a heat treatment of semiconductor single crystal substrates by radiant heating, a susceptor containing graphite as a chief material and coated with silicon carbide (SiC) is placed within a silica glass container. Then, semiconductor single crystal substrates are held on the susceptor while the back surface of each substrate is kept in close contact with the susceptor over the entire area thereof. The semiconductor single crystal substrates together with the susceptor are heated with radiant light emitted from a radiant heating means, such as an infrared lamp to thereby perform the heat treatment at a desired temperature.
However, the susceptor containing graphite as a chief material is often contaminated with metals, and it could be also water contaminated. As the temperature goes up by heating, the contaminants or impurities are released from the susceptor and admixed with a reaction gas or atmosphere. If the impurities were incorporated in the semiconductor single crystal substrates being heat treated, the quality of the semiconductor single crystal substrates would be deteriorated.
Furthermore, when an attempt is made to heat the semiconductor single crystal substrates uniformly over the entire area thereof by the use of the susceptor containing graphite as a chief material, the susceptor is required to have a greater size than the substrates to be heat treated. Since such a great susceptor has a large thermal capacity, it takes a long time to heat the susceptor to the desired temperature. The long heating time, however, affects the productivity and, accordingly, an appropriate improvement is needed.
To cope with this difficulty, it has been proposed a method in which semiconductor single crystal substrates are directly heated with radiant light emitted from infrared lamps, for example, while the substrates are disposed within a silica glass container, with a portion of the back surface or a portion of the periphery held in position without using a susceptor. The proposed method has a problem however that when the substrates are heated to the desired heat treating temperature, an ultimate temperature reached at this time varies depending on the individual substrates being heat treated.
From a close study and investigation of the phenomenon, in which direct heating of the back surface of semiconductor single crystal substrates with radiant light tends to vary the ultimate temperature of the individual substrates being heat treated, the present inventor has found that it is caused due to the reflectivity of the back surface of the semiconductor single crystal substrates which is variable with the individual substrates. Based on this finding, the present inventor has completed the present invention.
It is an object of the present invention to provide a heat treating method in which semiconductor single crystal substrates being heat treated are able to have a constant ultimate temperature, thereby making it possible to maintain a uniform crystal quality throughout the semiconductor single crystal substrates being heat treated, and a semiconductor single crystal substrate which is able to realize uniform heating easily by a radiant heating means.